Amplifiers – With pilot frequency control means
Reexamination Certificate
1999-10-14
2001-01-09
Pascal, Robert (Department: 2817)
Amplifiers
With pilot frequency control means
C330S151000
Reexamination Certificate
active
06172560
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an amplifier with feedforward (abbreviated hereinafter as FF) loops for rejecting non-linear distortion and control circuitry for optimizing FF loops which employs a method for compensating distortion generated in a main amplifier. The present invention particularly relates to a technique for compensating distortion such as intermodulation distortion generated in a main amplifier.
2. Description of Related Art
A base station or a relay station for mobile communications performs wireless transmission of a multicarrier signal including a number of modulated carriers. More specifically, a base station or a relay station modulates each of the multiple carriers and arranges those carriers on a frequency axis at a certain frequency separation to obtain a multicarrier signal. The base station or the relay station then executes radio-frequency amplification (RF amplification) of the obtained multicarrier signal, and performs wireless transmission of the multicarrier signal after the RF amplification. Accordingly, such a station requires an amplifier for executing RF amplification of a multicarrier signal. Further, in order to favorably communicate with a mobile station located within a coverage or a cell, the station typically requires a RF amplifier that can perform high power amplification. A similar need also exists in a booster or like devices.
In an amplifier used for amplifying a multicarrier signal, superior linearity is required over the entire frequency range to which the multicarrier signal belongs because, if the linearity of the amplifier is not sufficient, normal and high-quality communication would be obstructed by distortion generated in the amplifier. A variety of distortions exist that are caused by the non-linearity of the amplifier. Among those distortions, distortion being produced at a frequency identical to or extremely close to that of a carrier like IMD (intermodulation distortion) cannot be, or remains very difficult to be, eliminated by an approach such as providing a filter after the amplifier. Nevertheless, distortions having such nature are likely to occur when amplifying a multicarrier signal.
One approach for providing an amplifier having an extremely low amount of distortion which is suitable for amplifying a multicarrier signal is to improve the linearity of the amplifier by adding circuitry to the amplifier. One known example technique of such an approach is the FF amplification method disclosed in Japanese Patent Laid-Open Publication No. Hei 4-70203. An amplifier adopting the FF amplification method comprises a distortion detection loop and a distortion rejection loop.
The signal path from the signal input terminal to the signal output terminal passing through the main amplifier, that is, the signal path for transmitting the input signal into the main amplifier to be amplified and the signal amplified by the main amplifier, is referred to as the dominant path. To simplify notation in the present application, the signal transmitted in the dominant path is hereinafter referred to as the dominant signal. The signal passing through the dominant path before the main amplifier is referred to as the input signal. The signal passing through the dominant path from the output terminal of the main amplifier to the point of being subjected to distortion compensation is referred to as the output signal. The signal passing through the dominant path after the point of distortion compensation is referred to as the distortion-compensated output signal.
The distortion detection loop provides as a feedforward a first branch signal obtained by branching a portion of the input signal at a first branching point to a first coupling point located thereafter. At a second branching point located after the first branching point and a main amplifier, a portion of the output signal is branched as a second branch signal. The second branch signal and the first branch signal provided as a feedforward are combined at the first coupling point.
The input signal and the first branch signal branched therefrom include a plurality of carrier components constituting the multicarrier signal, but do not, at any time, include distortion components generated in the main amplifier or its surrounding circuitry (hereinafter collectively referred to as “the main amplifier”). On the other hand, when distortion components are being generated in the main amplifier, the output signal and the second branch signal branched therefrom include both the carrier components and the distortion components. Accordingly, when combining the first and the second branch signals, if the first and the second branch signals to be combined are in a relationship such that their respective carrier components cancel each other out, a signal including only the distortion components can be obtained. A signal obtained as such is hereinafter referred to as the distortion signal.
To obtain a highly pure distortion signal having only the distortion components, the first and the second branch signals must be in a relationship such that their respective carrier components completely cancel each other. Specifically, a first requirement for this relationship is that the electrical wave length of the signal path from the first branching point to the first coupling point passing through the distortion detection loop must be identical with the electrical wave length of the signal path from the first branching point to the first coupling point passing through the main amplifier and the second branching point. A second requirement is that, at the first coupling point, the first and the second branch signals must have an identical amplitude and an opposite phase from one another.
The distortion rejection loop provides the distortion signal as a feedforward to be recombined with the output signal at a second coupling point located after the first and the second branching points. If the signal delay occurring in the distortion rejection loop is compensated in the dominant path, and if the distortion components in the output signal and the distortion signal through the auxiliary amplifier are appropriately adjusted in the distortion rejection loop or in the dominant path such that their respective amplitudes are identical and their phases are opposite from one another, the signal recombining operation at the second coupling point rejects distortion components generated in the main amplifier to provide a distortion-compensated output signal having no, or a suppressed amount of, distortion components.
FIG. 8
shows an example configuration of a conventional FF amplifier. In this amplifier, three hybrids HYB
1
-HYB
3
are used to form the distortion detection loop L
1
and the distortion rejection loop L
2
. In the Figure, the signal path from the signal input terminal IN to the signal output terminal OUT passing through the main amplifier A
1
and the coaxial delay line D
2
is the dominant path. The signal path from the first branching point inside hybrid HYB
1
to the first coupling point inside hybrid HYB
2
passing through the coaxial delay line D
1
is the distortion detection loop L
1
. The signal path from the first coupling point to the second coupling point inside hybrid HYB
3
passing through the auxiliary amplifier (distortion amplifier) A
2
is the distortion rejection loop L
2
. Respective dummy loads Z
0
in the Figure have an impedance equal to the characteristic impedance of the transmission line, and is used as the termination for hybrids HYB
1
and HYB
3
terminals. The second branching point is located inside hybrid HYB
2
.
The signal applied to the signal input terminal IN, namely, the input signal, is a multicarrier signal, for example. This signal is input, via hybrid HYB
1
, into variable attenuator ATT
1
and variable phase shifter PS
1
. After being subjected to amplitude and phase adjustment therein, the input signal is amplified by the main amplifier A
1
. The signal amplified by the main amplifier A
1
, namely, the output signal
Nakagawa Yasushi
Yamada Akira
Yamashita Kazuo
Choe Henry
Japan Radio Co. Ltd.
Oliff & Berridg,e PLC
Pascal Robert
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